CN109136564B

CN109136564B - Treatment method of carbon-containing waste residues of electrolytic aluminum

Info

Publication number: CN109136564B
Application number: CN201810861698.4A
Authority: CN
Inventors: 陈湘清; 唐剑; 陈小松; 陈黎军; 娄世彬; 陈环月
Original assignee: Hunan Lvmai Environmental Protection Technology Co Ltd
Current assignee: Hunan Lvmai Environmental Protection Technology Co Ltd
Priority date: 2018-08-01
Filing date: 2018-08-01
Publication date: 2021-02-19
Anticipated expiration: 2038-08-01
Also published as: CN109136564A

Abstract

The invention belongs to the technical field of treatment of carbon-containing hazardous waste in electrolytic aluminum industry, and particularly discloses a method for treating carbon-containing waste residues of electrolytic aluminum. The method for treating the carbon-containing waste residue of the electrolytic aluminum comprises the steps of crushing the carbon-containing waste residue of the electrolytic aluminum, mixing the crushed carbon-containing waste residue with a catalyst during or after crushing, heating, oxidizing and calcining, oxidizing a carbon material in the carbon-containing waste residue material of the electrolytic aluminum, and obtaining a residual material which is a recovered fluorine-containing electrolyte product. By means of low-temperature oxidation gasification of the carbon materials contained in the carbon-containing waste residues, during the low-temperature oxidation process, the electrolyte does not react, the residues left after the carbon materials are completely oxidized are the electrolyte, and the problems that the smoke carries fluorides and corrodes equipment do not exist, the purpose of effectively separating the carbon materials from the electrolyte materials is achieved, and the effective recovery of the electrolyte materials in the electrolytic aluminum carbon-containing waste residues is achieved.

Description

Treatment method of carbon-containing waste residues of electrolytic aluminum

Technical Field

The invention relates to the technical field of treatment of carbon-containing hazardous waste in electrolytic aluminum industry, in particular to a method for treating carbon-containing waste residues of electrolytic aluminum.

Background

The hazardous waste containing carbon in the electrolytic aluminum comprises carbon slag, waste cathode carbon blocks (comprising carbon materials such as tamping paste and side carbon blocks), anode scrap cleaning materials, overhaul slag and the like, and is listed in national hazardous waste record-HW 48 non-ferrous metal smelting waste-salt slag and scum generated in the electrolytic aluminum process because of containing toxic substances such as soluble fluoride and the like. The carbon slag is formed in the electrolytic cell because carbon particles fall off due to the fact that the anode carbon block and the cathode carbon block are subjected to electrolyte erosion and washing for a long time, are combusted unevenly, are oxidized selectively, are unqualified in quality and the like in the production process of electrolytic aluminum. The carbon residue has high content of fluoride salt due to long-term soaking and permeation of electrolyteThe main components of the carbon slag, which account for about 60 to 70 percent of the weight of the carbon slag, are cryolite, cryolite and carbon, and the balance is alumina, sodium fluoride, calcium fluoride, magnesium fluoride, lithium fluoroaluminate, potassium fluoroaluminate and the like. According to statistics, about 10-15 kg of anode carbon slag is produced in each ton of raw aluminum, about 4490 ten thousand tons of aluminum electrolysis capacity in 2017 of China is produced, and about 674 ten thousand tons of anode carbon slag is produced. And (3) overhauling slag, wherein the aluminum electrolytic cell generally needs to be planed and overhauled due to serious damage after 5-8 years of operation, and planed furnace bottom materials are collectively called as overhauling slag. The overhaul slag mainly comprises waste cathode carbon blocks (containing steel bars) and waste refractory materials (refractory bricks, insulating bricks, dry type impermeable materials and the like). The waste cathode carbon block contains about 70% of carbon, part of the carbon is graphite carbon, and contains fluoride salt about 30%, mainly Na₃AlF₆、NaF、CaF₂NaCN, and a small amount of Al₂O₃And free metal impurities, etc. The components harmful to the environment in the waste cathode carbon block are as follows: NaF, readily water soluble, leaching F^-The harmfulness is extremely high; na (Na)₃AlF₆Easily decomposed by heating to generate NaF and AlF₃Therefore, has certain harmfulness; cyanide, with NaCN or Na₄[Fe(CN)₆]In the form of cyanide readily leaches CN when it comes into contact with water, although the content is very low, about 0.1-0.2%^-Reacting with water to release HCN, the cyanide is extremely toxic. The anode scrap is required to be used as a raw material to be mixed into the production of a new anode again, so that before the anode scrap is used, the surface electrolyte, the soft scrap and the steel claw rust of the anode scrap are required to be cleaned by iron shots, the generated waste residue is the scrap cleaning material or the shot blasting scrap cleaning material, and the main components and the contents of the waste residue are preliminarily estimated to be 40% of carbon powder, 55% of electrolyte, 5% of rust and iron shots and the like. The fluoride ion concentration of the leachate of such waste exceeds the standard of 100mg/L, also belonging to solid hazardous waste, because of the presence of electrolytes.

The main treatment methods of the carbon-containing hazardous waste of the electrolytic aluminum can be classified into a fire method process and a wet method process, and the following description is provided.

The fire process includes crushing carbon slag, cathode carbon block, etc., adding fluorine fixing agent, high temperature calcining in metallurgical furnace, rotary kiln and other apparatus to decompose or cure harmful matterIs harmless. Adopting a high-temperature calcination method for treatment, and burying after the fluoride undergoes a chemical reaction to generate a harmless substance; cyanide can be decomposed into N at a temperature higher than 700 deg.C₂And CO₂A gas. The carbon in the waste cathode is completely burnt as high-heating-value fuel at high temperature, thereby saving part of energy. The SPLIT process developed by Pechiney company is characterized by adding calcium sulfate and calcium oxide, carrying out two-stage treatment at 800-1800 ℃ to pyrolyze cyanide, using the finally produced solid material as a filling material, and establishing a treatment plant for treating 10000t of waste tank liners in the year. The 'COMTOR' process developed by Comalco aluminum Limited adopts a TORBED furnace for roasting, the treatment temperature is more than 550 ℃, the treated products comprise carbon powder, inert anode scrap, fluorite and Bayer process alkali liquor, and a treatment plant for treating 10000t of waste tank liners in year is established. The Alcan company developed the "LCLL" process, which uses hot lye and lime to decompose the waste cathode under pressure, the products being carbon powder, inert slag, bayer process lye and fluorite. A spent cathode treatment plant with a treatment capacity of 80000t/a is planned to be constructed. Chinese patent application No. 201610641427.9 also discloses a high temperature continuous process for disposing of spent cathodes of electrolytic aluminum. Similar pyrogenic processes are also disclosed, for example, in application nos. 201710128417.X, 201210511925.3, 201610565814.9, and the like. The method has the problems of equipment corrosion, fluoride-containing smoke, high energy consumption and the like in most treatment temperatures of 1200-2000 ℃, and has great defects in industrial application. Specifically, after the electrolyte fluoride is melted, the lining of the rotary kiln is corroded, the service life of equipment is influenced, and the volatilized hydrogen fluoride gas can cause secondary pollution; a purification device is required to be configured for reducing the pollution of the fluoride gas, so that the investment cost is high; the combustion temperature is high and uncontrolled, the electrolyte is melted, decomposed and volatilized (such as the melting point of the cryolite 696.2 ℃ in the electrolyte) to be liquid and gaseous, the carbon powder is wrapped by the liquid electrolyte, the oxidation is prevented, the treatment time is long, and the gaseous electrolyte cannot be recovered.

And wet process, namely flotation treatment process. The Qiu Zhuxian et al of northeast university is the earliest method for treating carbon slag and waste cathode carbon blocks by flotation,the process flow is as follows: the waste cathode carbon blocks are subjected to coarse crushing, medium crushing and fine crushing to prepare powder with the granularity of 100-150 meshes, the powder is subjected to pulping and enters a flotation machine, and a regulator, a collecting agent and a foaming agent are added. After flotation, carbon (floating foam) and solid electrolyte (underflow) are obtained, the carbon can be used for manufacturing a new cathode carbon block, and the electrolyte mainly comprises cryolite and alumina and can be returned for aluminum electrolysis. The university of Kunming technology adopts a caustic alkali leaching method, firstly, waste cathodes are crushed to the required granularity and are uniformly mixed, then, alkali leaching is firstly adopted, then, alkali leaching liquid is treated by a carbonization method, the solid after alkali leaching is washed and then treated by a flotation method, and various useful substances are recovered. For example, chinese patent application No. 201710918899.9 discloses a processing method of waste cathode carbon blocks for aluminum electrolysis. The Chinese patent application with the application number of 201610498578.3 discloses a method for recovering carbon in aluminum electrolysis waste cathodes by ultrasonic-assisted pressure acid leaching. Wet processing techniques are also disclosed, for example, in application nos. 201711215500.7, 201711099051.4, 201610224382.5, 201620301272.X, and the like. The method has the problems that the recovery rate of the electrolyte is low, the granularity is too fine, the carbon mud still contains about 20 percent of the electrolyte, the leaching toxicity of the partial waste residue still exceeds the standard, and the requirement of thorough harmlessness of the carbon residue cannot be met; the harmless treatment is not thorough, and the wet treatment can not avoid generating toxic gas HCN and combustible explosive gas CH₄(ii) a The produced regenerated products such as graphite, fluoride and the like have low purity; for example, the compressive strength of the waste cathode is as high as 40MPa, the crushing and ball milling difficulty is high, and the energy consumption of crushing equipment is high.

Based on the current situation, the application provides a novel method for treating the carbon-containing waste residue of the electrolytic aluminum.

Disclosure of Invention

The invention mainly solves the technical problem of providing a method for treating carbon-containing waste residues of electrolytic aluminum, which achieves the aim of effectively separating carbon materials from electrolyte materials in the carbon-containing waste residues of the electrolytic aluminum by low-temperature oxidation gasification of the carbon materials in the carbon-containing waste residues, wherein in the low-temperature oxidation process, the electrolyte does not react, the residues left after the carbon materials are completely oxidized are the electrolyte, and the problems that smoke contains fluoride and corrodes equipment do not exist.

In order to solve the technical problems, the invention adopts the technical scheme that: a method for treating carbon-containing waste residues of electrolytic aluminum comprises the following steps:

s1: crushing and mixing with catalyst

Crushing the carbon-containing waste residues of the electrolytic aluminum to be treated until the granularity is 0.01-500 mm, and mixing the crushed carbon-containing waste residues with a catalyst during or after the crushing; the catalyst is NaF, KF, NaCl, KCl, VCl₂And NiCl₂Any one or a mixture of several of them; in the industrial process, the purity requirement of the catalyst can be not strict, and the catalyst can remove effective components of NaF, KF, NaCl, KCl and VCl₂And/or NiCl₂In addition, certain impurities can be contained, so that the realization of the invention is not influenced;

s2: oxidative calcination

Oxidizing and calcining: and (S1) oxidizing and calcining the catalyst-mixed carbon-containing waste residue of the electrolytic aluminum at 300-690 ℃, wherein the oxidizing and calcining time is 2-60 hours, and the residual product after oxidizing and calcining is a recovered fluorine-containing electrolyte product.

Further, the catalyst can be directly mixed with the electrolytic aluminum carbon-containing waste residue to be treated in a solid form, or the catalyst can be mixed with water to prepare an aqueous solution and then mixed with the electrolytic aluminum carbon-containing waste residue to be treated.

Further, the amount of the catalyst is 1-50% of the weight of the electrolytic aluminum carbon-containing waste residue to be treated.

Further, in step S2, the catalyst-mixed electrolytic aluminum carbonaceous waste residue obtained in step S1 is preheated and then subjected to oxidizing calcination.

Preferably, the catalyst-mixed electrolytic aluminum carbon-containing waste residue obtained in step S1 is preheated by using the residual heat of the oxidation calcination stage.

Preferably, the preheating conditions of the catalyst-mixed electrolytic aluminum carbon-containing waste residue obtained in the step S1 are as follows: preheating is carried out at 300-350 ℃, and the preheating time is 30-240 minutes.

Preferably, the oxidizing calcination temperature is 500-690 ℃.

The treated carbon-containing waste residue of the electrolytic aluminum can be any one or a mixture of several of carbon residue, waste cathode carbon blocks, anode scrap cleaning materials, overhaul residues and carbon residue flotation carbon mud. The carbon residue flotation carbon mud refers to carbon mud obtained after the carbon residue is subjected to wet flotation treatment, and the carbon mud also contains about 20% of electrolyte.

Preferably, the oxidative calcination step is carried out in a tunnel kiln, pushed slab kiln, rotary kiln, shuttle kiln or metallurgical furnace. Metallurgical furnaces such as can furnaces or shaft furnaces.

Preferably, the flue gas after the oxidation calcination enters a cyclone separator or a bag-type dust collector for treatment, and the collected solid is a recovered fluorine-containing electrolyte product.

The invention provides a method for treating carbon-containing waste residue of electrolytic aluminum, which comprises the steps of crushing the carbon-containing waste residue of electrolytic aluminum with larger crushing granularity, and mixing the crushed carbon-containing waste residue with a catalyst, wherein the catalyst is NaF, KF, NaCl, KCl or VCl₂、NiCl₂And (2) alkali metal, vanadium and nickel chloride are added, heating, oxidizing and calcining are carried out, the electrolytic aluminum carbon-containing waste residue material mixed with the catalyst is fed into a furnace type such as a tunnel kiln, a pushed slab kiln, a rotary kiln, a shuttle kiln or a metallurgical furnace, natural gas or water gas is taken as fuel, the material is oxidized at the temperature of 300-690 ℃ under the combustion supporting of air or oxygen, the carbon material in the electrolytic aluminum carbon-containing waste residue is oxidized, and the residual material obtained after oxidation is the recovered fluorine-containing electrolyte product.

In order to further improve the effect, the electrolytic aluminum carbon-containing waste residue material mixed with the catalyst is fed into a furnace type such as a tunnel kiln, a pushed slab kiln, a rotary kiln, a shuttle kiln or a metallurgical furnace, natural gas or water gas is taken as fuel, the material is preheated by circulating flue gas under the combustion supporting of air or oxygen, the preheating temperature is 300-. After preheating, oxidizing and calcining are carried out, so that the carbon materials in the electrolytic aluminum carbon-containing waste residue material are removed more thoroughly, and the recovered fluorine-containing electrolyte product has higher purity.

The treatment principle of the treatment method of the carbon-containing waste residue of the electrolytic aluminum provided by the invention is as follows: the carbon material in the carbon-containing waste residue can be oxidized at the temperature of more than 500 ℃, and after the electrolytic aluminum carbon-containing waste residue is mixed with the catalyst, the oxidation of the carbon material in the carbon-containing waste residue at low temperature can be accelerated (the reason is that after the catalyst is added, elements such as sodium, potassium, vanadium, nickel and the like in the catalyst can reduce the carbon oxidation activation energy, so that the initial oxidation temperature of the carbon material is lowered or the oxidation rate is accelerated at the same temperature, and the catalyst can be decomposed at high temperature to generate F₂And/or Cl₂Gas, the material is loosened and porous, the material is in full contact with the gas, and the reaction efficiency is obviously improved), and the electrolyte contained in the carbon-containing waste residue can be melted and volatilized until the temperature is more than 700 ℃, so the temperature is not higher than 700 ℃ through the controlled oxidation and gasification of the carbon material contained in the carbon-containing waste residue, the residue left after the carbon material is completely oxidized is the electrolyte, and the electrolyte does not react in the low-temperature oxidation process, so the problems of fluoride in flue gas and equipment corrosion do not exist, and the aim of effectively separating the carbon material from the electrolyte material is fulfilled. The method for treating the carbon-containing waste residues of the electrolytic aluminum, provided by the invention, has the advantages of simple treatment method and low cost, can realize the basic and complete recovery of the electrolyte in the carbon-containing waste residues, has high purity of the recovered electrolyte, provides an important premise for the effective utilization of the electrolyte, and has important significance in the treatment of carbon-containing hazardous wastes in the electrolytic aluminum industry.

The technical scheme of the invention has the following advantages:

1. the heat of carbon oxidation in the waste residue is effectively utilized, the energy consumption is low, and the operation cost is low;

2. the raw materials do not need to be ground, and the granularity of the recovered electrolyte is large;

3. the electrolyte is solid in the whole treatment process, so that the fluoride gas emission is less, and the corrosion to equipment is low;

4. the recovery rate of the electrolyte in the waste residue is high and exceeds 99 percent, and resources are effectively utilized;

5. the catalyst is utilized to accelerate the medium-low temperature oxidation of the carbon material in the carbon-containing waste residue.

Detailed Description

The technical solution of the present invention will be described in detail by specific examples.

Example 1

And (4) treating the carbon slag by adopting a tunnel kiln.

Crushing carbon slag, and spraying catalytic liquid for 5min, wherein the catalytic liquid comprises the following components in percentage by mass: NaCl 15%, KCl 10%, NaF 5%, VCl₂1 percent and the balance of water, a 35-meter long tunnel kiln is adopted, the propelling speed of a kiln car is 2.2 h/car, the loading amount is 660kg, the pretreatment section is 10 meters, the temperature is 350 ℃, the oxidation section is 15 meters, the temperature is controlled at 670-680 ℃, the slag discharging section is carried out after 12h of oxidation, the weight of oxidized residues is 528kg, the residues are mainly fluoride, and the detection indexes are shown in table 1.

TABLE 1

Example 2

And (3) treating the carbon residue flotation carbon mud by adopting a tunnel kiln.

Spraying the flotation carbon mud for 5min by using a catalytic liquid, wherein the catalytic liquid comprises the following components in percentage by mass: NaCl 18%, KCl 5%, NaF 15%, VCl₂1 percent and the balance of water, a 50-meter long tunnel kiln is adopted, the propelling speed of a kiln car is 1.5 h/car, the loading amount is 650kg, the pretreatment section is 10 meters, the temperature is 350 ℃, the oxidation section is 20 meters, the temperature is controlled to be 650 plus 685 ℃, residue is discharged after being oxidized for 10h, the oxidized residue is 390kg, the residue is mainly fluoride, and the detection index is shown in table 2.

TABLE 2

Example 3

And (4) treating the anode scrap cleaning material by adopting a rotary kiln.

Spraying the anode scrap cleaning material for 8min by using a catalytic liquid, wherein the catalytic liquid comprises the following components in percentage by mass: NaCl 12%, KCl 6%, NaF 7%, VCl₂2 percent and the balance of water, a rotary kiln with the length of 60 meters is adopted, the rotating speed of the rotary kiln is 0.4r/min, the loading amount is 650kg, the pretreatment section is 10 meters, the temperature is 350 ℃, the oxidation section is 32 meters, the temperature is controlled to be 650 plus materials and 685 ℃, residue discharge is carried out after oxidation is carried out for 8 hours, the oxidized residue weighs 390kg, the residue is mainly fluoride and iron impurities, and the detection indexes are shown in Table 3.

TABLE 3

Example 4

And (4) treating the waste cathode carbon blocks by adopting a pot furnace.

Spraying catalytic liquid for 1min on the grooved cathode block, wherein the catalytic liquid comprises the following components in percentage by mass: 11% of NaCl, 3% of KCl, 9% of NaF and NiCl₂1 percent of water and 3600kg of water, adopting a 6-layer flame path pot furnace, firstly controlling the temperature to be 300-.

TABLE 4

The pot furnace is not divided into a preheating section, the temperature is set as the temperature of the preheating section, materials are not moved in the preheating section, preheating is firstly carried out, and then the temperature is increased for oxidation.

Example 5

And (3) treating the waste cathode carbon blocks by using a shaft furnace.

The size of the cathode block after the steel bar is cleaned is 100-500mm, and the catalytic liquid is sprayed for 1min, wherein the catalytic liquid comprises the following components in percentage by mass: 8% of NaCl, 6% of KCl, 2% of NaF and VCl₂ 2％，And the balance of water is oxidized by adopting a shaft furnace, the charging amount is 4530kg, the waste cathode block is charged from the top of the shaft furnace and stays at a preheating layer firstly, a plurality of layers of brackets are arranged on the preheating layer, the brackets are provided with free opening and closing mechanisms and can control the cathode block to gradually move from top to bottom, a burner is arranged in a combustion chamber at the bottom of the shaft furnace, the temperature is controlled to be 300-plus-material 350 ℃, the preheating is carried out for 30 minutes, the temperature is controlled to be 590-plus-material 690 ℃, the waste cathode block is discharged from the furnace after 22 hours of oxidizing and calcining, oxidized residues fall to the bottom and weigh 1268kg, the residues are mainly fluorides.

TABLE 5

The carbon-containing waste residues of the electrolytic aluminum treated in the above examples 1 to 5 are one of carbon residue, waste cathode carbon block, anode scrap cleaning material, overhaul residue and carbon residue flotation carbon sludge. It will be appreciated that mixtures of two or more of carbon residue, spent cathode carbon blocks, anode scrap cleaning material, overhaul debris and carbon residue flotation carbon sludge may also be treated using the methods of the above examples.

The above description is only an example of the present invention, and is not intended to limit the scope of the present invention, and all equivalent modifications made by the present invention in the specification or other related fields directly or indirectly are included in the scope of the present invention.

Claims

1. The method for treating the carbon-containing waste residue of the electrolytic aluminum is characterized by comprising the following steps of:

s1: crushing and mixing with catalyst

Crushing the carbon-containing waste residues of the electrolytic aluminum to be treated until the granularity is 0.01-500 mm, and mixing the crushed carbon-containing waste residues with a catalyst during or after the crushing; the catalyst is NaF, KF, NaCl, KCl, VCl₂And NiCl₂Any one or a mixture of several of them; the catalyst is NaCl, KCl, NaF and VCl₂The compositions in percentage by mass are respectively as follows: 15%, 10%, 5%, 1%, 18%, 5%, 15%, 1%, 12%, 6%7%, 2% or 8%, 6%, 2% aqueous solution, or NaCl, KCl, NaF and NiCl₂The compositions in percentage by mass are as follows: 11%, 3%, 9%, 1% aqueous solution;

s2: oxidative calcination

Oxidizing and calcining: and (S1) oxidizing and calcining the catalyst-mixed carbon-containing waste residue of the electrolytic aluminum at 500-690 ℃, wherein the oxidizing and calcining time is 2-60 hours, and the residual product after oxidizing and calcining is a recovered fluorine-containing electrolyte product.

2. The method for treating the carbon-containing waste residue of the electrolytic aluminum according to claim 1, wherein the amount of the catalyst is 1-50% of the weight of the carbon-containing waste residue of the electrolytic aluminum to be treated.

3. The method of claim 1, wherein in step S2, the catalyst-mixed carbon-containing waste residue of electrolytic aluminum obtained in step S1 is preheated and then oxidized and calcined.

4. The method for processing the electrolytic aluminum carbon-containing waste residue as claimed in claim 3, wherein the electrolytic aluminum carbon-containing waste residue mixed with the catalyst obtained in the step S1 is preheated by using the residual heat of the oxidation and calcination stage.

5. The method for treating the carbon-containing waste residue of electrolytic aluminum according to claim 4, wherein the carbon-containing waste residue of electrolytic aluminum mixed with the catalyst obtained in step S1 is preheated at 300-350 ℃ for 30-240 minutes.

6. The method for treating the carbon-containing waste residue of the electrolytic aluminum according to claim 1, wherein the carbon-containing waste residue of the electrolytic aluminum is any one or a mixture of several of carbon residue, waste cathode carbon block, anode scrap cleaning material, overhaul residue and carbon residue flotation carbon mud.

7. The method for treating carbon-containing waste residue of electrolytic aluminum as claimed in claim 1, wherein the step of oxidizing calcination is carried out in a tunnel kiln, a pusher kiln, a rotary kiln, a shuttle kiln or a metallurgical furnace.

8. The method for treating the carbon-containing waste residue of the electrolytic aluminum according to claim 1, wherein the flue gas after the oxidation and calcination enters a cyclone separator or a bag-type dust collector, and the collected solid is a product for recovering fluorine-containing electrolyte.